4Q DE. W. G. EIDEWOOD OlS" THE 



same horses from 9 a.m. till 9.30 p.m., without halting more than 

 a few minutes, none of them being apparently the wor^e for it, 

 and a sucking foal following its mother during the whole journey. 

 The horse which I rode accomplished the last hour of the journey 

 at a canter in the dark. 



In conclusion 1 would strongly urge upon any one who may 

 think of visiting the country, that a knowledge of the Eussian 

 language is almost indispensable; and considering the large 

 amount of valuable material which is practically buried in 

 Eussian scientific journals, I am surprised that so few English 

 naturalists have hitherto thought it worth their while to do 

 Avhat many young Army Officers, for military purposes, now do 

 every year. 



Some Observations on the Caudal Diplospondyly of Sharks. 

 By W. Gr. EiDEWooD, D.Sc, F.L.S., Lecturer on Biology 

 at St. Mary's Hospital Medical School, Loudon. 



[Eead lOth January, 1899.] 



It is a well-known fact in Ichthyology that in Selachian fishes 

 the vertebrae of the tail are twice as numerous as the caudal 

 segments, delimited by the spinal nerves and the intermuscular 

 septa. 



The first clear reference to this remarkable phenomenon occurs, 

 curiously enough, in Grotte's memoir on the development of the 

 rire-bellied Toad (Bomhinafor), (6. p. 418, footnote). It has 

 since been remarked upon by von Ihering (9. pp. 220-236), 

 Basse (7. p. 21), Balfour (1. p. 455), Schmidt (15. p. 756), Mayer 

 (13. pp. 262-267), Gadow (4. pp. 194-196), and others. 



To each myomere and neuromere there occur two centra, two 

 pairs of crural plates, two pairs of intercrural plates, and four 

 neural spines. The two centra are similar*, as also are the 

 hfemal arches and the neural spines, but the crural plates are 

 alternately imperforate and perforated by the ventral nerve-root, 

 While a similar relation exists between the intercrural plates and 



* Except in Galeus, in which they are alternately slightly longer and 

 shorter. 



